In a base station, a radio remote unit (RRU), a standing wave detection system and a feed system, a coupling device is generally used to check the signal power. Circuitry of an existing coupling device is shown as in FIG. 1, where J2 and J1 are respectively an input terminal and an output terminal for main signals, J3 an output terminal for coupling signals, J4 an isolation terminal, and Coupler the coupling portion of the coupling device. The coupling portion may be in the form of coupling sheet—metal main rod or microstrip line—metal main rod, and so on. An adjustable circuit for adjusting the coupling degree or isolation degree is respectively disposed at the coupling signal output terminal and isolation terminal. The adjustable circuit is mainly comprised of a capacitor, an inductor, a resistor, a tunable potentiometer, a variable capacitor, etc. It is configured to compensate for errors derived from machining accuracy of printed circuit board (PCB) or metal cavity, and errors derived from installation processes, and so on. Such a coupling device has the following drawbacks:
1. To achieve the required isolation specification and coupling specification, a coupling terminal adjustable circuit and an isolation terminal adjustable circuit would be needed. In actual tuning process, however, tuning the isolation terminal adjustable circuit will largely influence the coupling degree, while tuning the coupling terminal adjustable circuit will also influence the isolation degree, causing the tuning difficult.
2. With the increasement of the device's operating time, some adjusting components may be aging fast. The coupler may deteriorate dramatically in its performance, and even result in failure, causing communication failure of the device; components applied in the adjustable circuit may reduce the reliability of the device, thus increasing the failure rate of the device; components applied in the adjustable circuit may undergo wide parameters variation through high and low temperatures, thus making the communication device difficult to maintain a good working condition under various temperature environments; introduction of the adjustable circuit may lift up the raw material cost and production cost of the device.
Another existing coupling device is also available, in which an adjustment mechanism may be utilized to adjust the distance and angle between the coupling sheet and the metal main rod, thus achieving the adjustment of coupling amount of the coupling sheet and the adjustment of the signal phase. However, the circuit on the printed circuit board that is connected to the coupling circuit board is fixedly arranged, thus, the connections between the coupling sheet and other circuits may be unstable when the coupling sheet rotates, and implementations of which may be relatively complex, resulting in poor reliability of the coupling device.